1. Field of the Invention
This invention relates to a method and an apparatus for inspecting the airtightness of a gas sensor used in, for example, control of the burning of an air-fuel mixture in an internal combustion engine.
2. Description of the Related Art
Japanese patent application publication number 10-10082 discloses a gas sensor designed to enhance the degree of the sealing between a metal fitting body and a sensor element. In the gas sensor of Japanese application 10-10082, a sealant is provided between an inner circumferential surface of a body and an outer circumferential surface of the sensor element. The sealant is pressed by an insulating member. An annular spring is coaxially located between the insulating member and a flange of a cylinder. An edge of a rear end of the body is bent inward to cover the flange of the cylinder, and is axially deformed to compress the sealant. A rear end face of the insulating member presses an inner portion of a front end face of the annular spring along an axial direction while a front end face of the flange of the cylinder presses an outer portion of a rear end face of the annular spring in the axial direction. Thus, the annular spring is resiliently deformed, continuously urging the insulating member in the direction of compressing the sealant.
Another known gas sensor includes a sub assembly in which a gas sensor element having a reference gas chamber is disposed. The sub assembly has a base end side covered with an atmosphere-side cover surrounded by an atmosphere. The atmosphere-side cover defines an atmosphere chamber filled with the atmosphere. The gas sensor element is exposed to a measurement gas introduced into a measurement gas chamber extending in the sub assembly. The atmosphere is introduced into the reference gas chamber as a reference gas via, for example, holes provided through the walls of the atmosphere-side cover. The measurement gas chamber and the atmosphere chamber are airtightly isolated from each other. Therefore, the introduced measurement gas and the introduced atmosphere are airtightly separated from each other. The gas sensor element has a first electrode exposed to the measurement gas, and a second electrode exposed to the reference gas (the atmosphere). A specific-component concentration in the measurement gas is detected on the basis of an electrochemical reaction occurring between the first and second electrodes. During the manufacture of the known gas sensor, the airtightness of the isolation between the measurement gas chamber and the atmosphere chamber is inspected.
It is a first object of this invention to provide an improved apparatus for inspecting the airtightness of a gas sensor.
It is a second object of this invention to provide an improved method of inspecting the airtightness of a gas sensor.
A first aspect of this invention provides an apparatus for inspecting the airtightness of a gas sensor. The gas sensor includes a gas sensor element, a sub assembly, and an atmosphere-side cover, the gas sensor element having a reference gas chamber and being disposed in the sub assembly, the atmosphere-side cover covering a base end side of the sub assembly and defining an atmosphere chamber extending outward of the sub assembly, the sub assembly having a measurement gas chamber therein, the gas sensor element being exposed in the measurement gas chamber, the atmosphere chamber communicating with the reference gas chamber, the atmosphere chamber and the measurement gas chamber being airtight isolated from each other. The apparatus operates for inspecting the airtightness of the isolation between the atmosphere chamber and the measurement gas chamber. The apparatus comprises an atmosphere-side jig located at the base end side of the sub assembly; and a measurement gas-side jig located at a distal end side of the sub assembly; wherein the measurement gas-side jig includes (1) an air chamber into which the distal end side of the sub assembly extends and which communicates with the measurement gas chamber, (2) a first socket receiving the sub assembly whose distal end side extends into the air chamber, and (3) a high-pressure air source supplying a high-pressure air to the air chamber; and wherein the atmosphere-side jig includes (1) a sealed chamber into which the base end side of the sub assembly extends and which communicates with the atmosphere chamber, (2) a second socket receiving the sub assembly whose base end side extends into the sealed chamber, (3) an airtight sealing portion providing airtight contact between the second socket and the sub assembly, (4) a low-pressure air source supplying the sealed chamber with a pressure lower than a pressure of the high-pressure air supplied to the air chamber, and (5) a sensor portion leading to the sealed chamber.
A second aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the sensor portion includes a first pipe connected between the low-pressure air source and the sealed chamber, a first valve provided in the first pipe, a second pipe having a first end connected with the low-pressure air source and a second end being closed, a third pipe connected between the first pipe and the second pipe, and a diaphragm provided in the third pipe.
A third aspect of this invention provides a method of inspecting the airtightness of a gas sensor. The gas sensor includes a gas sensor element, a sub assembly, and an atmosphere-side cover, the gas sensor element having a reference gas chamber and being disposed in the sub assembly, the atmosphere-side cover covering a base end side of the sub assembly and defining an atmosphere chamber extending outward of the sub assembly, the sub assembly having a measurement gas chamber therein, the gas sensor element being exposed in the measurement gas chamber, the atmosphere chamber communicating with the reference gas chamber, the atmosphere chamber and the measurement gas chamber being isolated from each other in an airtight manner. The method is of inspecting the airtightness of the isolation between the atmosphere chamber and the measurement gas chamber. The method comprises the steps of supplying high-pressure air to a distal end side of the sub assembly to introduce the high-pressure air into the measurement gas chamber; applying a low pressure to the base end side of the sub assembly to supply the low pressure to the atmosphere chamber, the low pressure being lower than a pressure of the high-pressure air introduced into the measurement gas chamber; and monitoring a variation in a pressure in the atmosphere chamber to detect an air leakage from the measurement gas chamber into the atmosphere chamber.
A fourth aspect of this invention is based on the third aspect thereof, and provides a method wherein the step of supplying the high-pressure air follows the step of applying the low pressure.
A fifth aspect of this invention provides an apparatus for inspecting the airtightness of a gas sensor. The gas sensor includes a first chamber for containing a reference gas during actual use of the gas sensor, and a second chamber for containing a measurement gas during actual use of the gas sensor. The apparatus comprises first means for applying a predetermined pressure to the second chamber; and second means for monitoring a pressure in the first chamber to detect an air leakage from the second chamber into the first chamber when the first means applies the predetermined pressure to the second chamber.
A sixth aspect of this invention provides an apparatus for inspecting the airtightness of a gas sensor. The gas sensor includes a first chamber for containing a reference gas during actual use of the gas sensor, and a second chamber for containing a measurement gas during actual use of the gas sensor. The apparatus comprises a pressure source generating a first predetermined pressure; first means for connecting the first chamber with the pressure source to subject the first chamber to the first predetermined pressure; second means for disconnecting the first chamber from the pressure source after the first means connects the first chamber with the pressure source; third means for applying a second predetermined pressure higher than the first predetermined pressure to the second chamber; and fourth means for monitoring a difference between a pressure in the first chamber and the first predetermined pressure to detect an air leakage from the second chamber into the first chamber after the second means disconnects the first chamber from the pressure source and when the third means applies the second predetermined pressure to the second chamber.